System and process for production of polyvinyl chloride

ABSTRACT

A method is disclosed for producing polyvinyl chloride which includes mixing a vinyl chloride solution with an initiator solution in at least one high shear mixing device comprising at least one rotor/stator set producing a rotor tip speed of at least 5.1 m/sec (1000 ft/min), to form a polymerization mixture; and allowing the mixture to polymerize by free radical polymerization to form polyvinyl chloride. The polymerization mixture may be subjected to free radical polymerization conditions comprising a temperature in the range of about 20° C. to about 230° C. In some embodiments, the high shear mixing device produces a shear rate of at least 20,000 s −1 . A system for carrying out the method is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/141,193 filed Jun. 18, 2008 which claims the benefit under 35 U.S.C.§ 119(e) of U.S. Provisional Patent Application No. 60/946,461 filedJun. 27, 2007; the disclosures of both of said applications are herebyincorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

TECHNICAL FIELD

The present invention generally relates to the liquid phasepolymerization of vinyl chloride to form polyvinyl chloride. Moreparticularly, the invention relates to apparatus and methods forproducing polyvinyl chloride which employ high shear mixing of thereactants.

BACKGROUND

Polyvinyl chloride (PVC) is a thermoplastic polymer that is widely usedin the manufacture of a variety of commercial products, includingbuilding materials, plumbing pipe, clothing, upholstery, flooring andvinyl records, to name just a few examples. PVC is synthesized by freeradical polymerization of vinyl chloride monomer using a monomer-solubleinitiator or catalyst. Some of the known initiators areazobisisobutyronitrile, tertiary butyl hydroperoxide, lauroyl peroxide,benzoyl peroxide and isopropylperoxy dicarbonate. A batch suspensionpreparation generally contains about 0.01 to 1.0 wt % vinyl chloridemonomer at a pH of about 7-9. Polymerization is commenced by dissolvingthe initiator in the monomer solution and heating at a temperature inthe range of about 35° to 75° C. for about 2 to 12 hours, with constantagitation of the reactants. The process is completed when one of thedetached hydrogen atoms attaches to the unpaired electron at the end ofthe PVC chain, or when the carbon atoms form a double bond through aprocess called disproportionation, which results in the free hydrogenatom.

The free radical polymerization of vinyl chloride monomer is generallyconsidered to be the easiest and most economical method today ofsynthesizing PVC, despite the fact that the polymerization process canalso cause impurities and defects in the polymer. Due to theunpredictable nature of free radical polymerization carbon-hydrogenbonds are sometimes broken instead of only the carbon-carbon bonds ofthe monomers, leading to the occurrence of branching at sites on thegrowing polymer strand where the carbon-hydrogen bond was broken.Another challenge associated with some PVC synthesis reactions is theamount of unpolymerized monomer that sometimes remains after thepolymerization reaction ceases. Many existing processes and productionfacilities for producing polyvinyl chloride are also subject to variousconstraints such as mass flow limitations, product yield, plant size andenergy consumption. Accordingly, there is continuing interest indeveloping ways to improve the selectivity and yield of polyvinylchloride from free radical polymerization of vinyl chloride monomer.

SUMMARY

In accordance with certain embodiments of the invention, a method isprovided for producing polyvinyl chloride. The method comprises mixing avinyl chloride solution with an initiator solution in a high shearmixing device comprising at least one rotor/stator set producing a rotortip speed of at least 5.1 m/sec (1,000 ft/min), to form a polymerizationmixture; and allowing the mixture to polymerize by free radicalpolymerization to polyvinyl chloride. In some embodiments, thepolymerization mixture is subjected to free radical polymerizationconditions comprising a temperature in the range of about 20° C. toabout 230° C. In some embodiments, the high shear mixing device producesa shear rate of at least 20,000 s⁻¹.

In accordance with another embodiment of the invention, a system isprovided which comprises a high shear mixing device comprising at leastone rotor/stator set configured to yield a rotor tip speed of at least5.1 m/sec (1,000 ft/min); a pump in fluid communication with an inlet ofthe high shear mixing device; and a vessel in fluid communication withan outlet of the high shear mixing device and configured for maintaininga predetermined pressure and temperature. In some embodiments, the highshear mixing device produces a shear rate of at least 20,000 s⁻¹. Theseand other embodiments and potential advantages will be apparent in thefollowing detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process flow diagram of a process for production ofpolyvinyl chloride, in accordance with an embodiment of the presentinvention.

FIG. 2 is a longitudinal cross-section view of a multi-stage high sheardevice, as employed in an embodiment of the system of FIG. 1.

DETAILED DESCRIPTION

The present methods and systems for the production of polyvinyl chloride(PVC), via liquid phase free radical polymerization of vinyl chlorideemploy an external high shear mechanical device to provide rapid contactand mixing of chemical ingredients in a controlled environment in thehigh shear mixer device and/or separate reactor. The high shear devicereduces the mass transfer limitations on the reaction and thus increasesthe overall reaction rate.

Chemical reactions involving liquids, gases and solids rely on the lawsof kinetics that involve time, temperature, and pressure to define therate of reactions. In cases where it is desirable to react two or moreraw materials of different phases (e.g. solid and liquid; liquid andgas; solid, liquid and gas), one of the limiting factors in controllingthe rate of reaction involves the contact time of the reactants. In thecase of heterogeneously catalyzed reactions there is the additional ratelimiting factor of having the reacted products removed from the surfaceof the catalyst to enable the catalyst to catalyze further reactants.Contact time for the reactants and/or catalyst is often controlled bymixing which provides contact with two or more reactants involved in achemical reaction. Homogeneous reactions may also benefit from highshear mixing, as disclosed herein, by at least providing uniformtemperature distribution within the reactor and minimizing potentialside reactions. Accordingly, in some embodiments, a high shear processas described herein promotes homogeneous chemical reaction(s).

A reactor assembly that comprises an external high shear device or mixeras described herein makes possible decreased mass transfer limitationsand thereby allows the reaction to more closely approach kineticlimitations. When reaction rates are accelerated, residence times may bedecreased, thereby increasing obtainable throughput. Product yield maybe increased as a result of the high shear system and process.Alternatively, if the product yield of an existing process isacceptable, decreasing the required residence time by incorporation ofsuitable high shear may allow for the use of lower temperatures and/orpressures than conventional processes. In some cases, it may be possibleto reduce the reactor size while maintaining the same product yield.

System for Production of Polyvinyl Chloride

A high shear system will now be described in relation to FIG. 1, whichis a process flow diagram showing an embodiment of a high shear system 1for the production of polyvinyl chloride by catalyzed polymerization ofthe corresponding monomer. The basic components of the system includeexternal high shear mixing device (HSD) 40, vessel 10, and pump 5. Asshown in FIG. 1, the high shear device is located external tovessel/reactor 10. Each of these components is further described in moredetail below. Line 21 is connected to pump 5 for introducing the vinylchloride monomer solution. Line 13 connects pump 5 to HSD 40, and line18 connects HSD 40 to vessel 10. Line 22 is connected to line 13 forintroducing an initiator (e.g., an organic peroxide) or catalyst in asuitable solvent. Line 17 is connected to vessel 10 for removal of ventgas. Additional components or process steps (e.g., recycling ofunreacted monomer) may be incorporated between vessel 10 and HSD 40, orahead of pump 5 or HSD 40, if desired.

High Shear Mixing Device. External high shear mixing device (HSD) 40,also sometimes referred to as a high shear mixer, is configured forreceiving an inlet stream via line 13, comprising a monomer andinitiator stream. Alternatively, HSD 40 may be configured for receivingthe monomer and initiator streams via separate inlet lines (not shown).Although only one high shear device is shown in FIG. 1, it should beunderstood that some embodiments of the system may have two or more highshear mixing devices arranged either in series or parallel flow. HSD 40is a mechanical device that utilizes one or more generators comprising arotor/stator combination, each of which having a fixed gap between thestator and rotor. HSD 40 is configured in such a way that it is capableof producing a dispersion containing submicron (i.e., less than onemicron in diameter) and micron-sized particles containing catalystdispersed in a liquid medium flowing through the mixer. The high shearmixer comprises an enclosure or housing so that the pressure andtemperature of the reaction mixture may be controlled.

High shear mixing devices are generally divided into three generalclasses, based upon their ability to mix fluids. Mixing is the processof reducing the size of particles or inhomogeneous species within thefluid. One metric for the degree or thoroughness of mixing is the energydensity per unit volume that the mixing device generates to disrupt thefluid particles. The classes are distinguished based on delivered energydensity. Three classes of industrial mixers having sufficient energydensity to consistently produce mixtures or dispersions with particlesizes in the range of submicron to 50 microns include homogenizationvalve systems, colloid mills and high speed mixers. In the first classof high energy devices, referred to as homogenization valve systems,fluid to be processed is pumped under very high pressure through anarrow-gap valve into a lower pressure environment. The pressuregradients across the valve and the resulting turbulence and cavitationact to break-up any particles in the fluid. These valve systems are mostcommonly used in milk homogenization and can yield average particlesizes in the 0-1 micron range.

At the opposite end of the energy density spectrum is the third class ofdevices referred to as low energy devices. These systems usually havepaddles or fluid rotors that turn at high speed in a reservoir of fluidto be processed, which in many of the more common applications is a foodproduct. These low energy systems are customarily used when averageparticle sizes of greater than 20 microns are acceptable in theprocessed fluid.

Between the low energy devices and homogenization valve systems, interms of the mixing energy density delivered to the fluid, are colloidmills, which are classified as intermediate energy devices. A typicalcolloid mill configuration includes a conical or disk rotor that isseparated from a complementary, liquid-cooled stator by aclosely-controlled rotor-stator gap, which is commonly between about0.0254 mm and about 10.16 mm (about 0.001-0.40 inch). Rotors are usuallydriven by an electric motor through a direct drive or belt mechanism. Asthe rotor rotates at high rates, it pumps fluid between the outersurface of the rotor and the inner surface of the stator, and shearforces generated in the gap process the fluid. Many colloid mills withproper adjustment achieve average particle sizes of 0.1-25 microns inthe processed fluid. These capabilities render colloid mills appropriatefor a variety of applications including colloid and oil/water-basedemulsion processing such as that required for cosmetics, mayonnaise, orsilicone/silver amalgam formation, to roofing-tar mixing.

An approximation of energy input into the fluid (kW/L/min) can beestimated by measuring the motor energy (kW) and fluid output (L/min).Tip speed is the circumferential distance traveled by the tip of therotor per unit of time. Tip speed is thus a function of the rotordiameter and the rotational frequency. Tip speed (in meters per minute,for example) may be calculated by multiplying the circumferentialdistance transcribed by the rotor tip, 2πR, where R is the radius of therotor (in meters, for example) times the frequency of revolution (inrevolutions per minute). A colloid mill, for example, may have a tipspeed in excess of 22.9 m/sec (4500 ft/min) and may exceed 40 m/sec(7900 ft/min). For the purposes of this disclosure, the term “highshear” refers to mechanical rotor stator devices (e.g., colloid mills orrotor/stator mixers) that are capable of tip speeds in excess of 5.1m/sec. (1000 ft/min) and require an external mechanically driven powerdevice to drive energy into the stream of materials to be reacted. Forexample, in HSD 40, a tip speed in excess of 22.9 m/sec (4500 ft/min) isachievable, and may exceed 40 m/sec (7900 ft/min). In some embodiments,HSD 40 is capable of delivering at least 300 L/h with a powerconsumption of about 1.5 kW at a nominal tip speed of at least 22.9m/sec (4500 ft/min).

HSD 40 combines high tip speeds with a very small shear gap to producesignificant shear on the material being processed. The amount of shearwill be dependent on the viscosity of the fluid. Accordingly, a localregion of elevated pressure and temperature is created at the tip of therotor during operation of the high shear device. In some cases thelocally elevated pressure is about 1034.2 MPa (150,000 psi). In somecases the locally elevated temperature is about 500° C. In some casesthese local pressure and temperature elevations may persist for nano orpico seconds. In some embodiments, the energy expenditure of the highshear mixer is greater than 1000 W/m³. In embodiments, the energyexpenditure of HSD 40 is in the range of from about 3000 W/m³ to about7500 W/m³. The shear rate is the tip speed divided by the shear gapwidth (minimal clearance between the rotor and stator). The shear rategenerated in HSD 40 may be greater than 20,000 s⁻¹. In some embodimentsthe shear rate is at least 1,600,000 s⁻¹. In embodiments, the shear rategenerated by HSD 40 is in the range of from 20,000 s⁻¹ to 100,000 s⁻¹.For example, in one application the rotor tip speed is about 40 m/sec(7900 ft/min) and the shear gap width is 0.0254 mm (0.001 inch),producing a shear rate of 1,600,000 s⁻¹. In another application therotor tip speed is about 22.9 m/sec (4500 ft/min) and the shear gapwidth is 0.0254 mm (0.001 inch), producing a shear rate of about 902,000s⁻¹.

HSD 40 is capable of highly mixing the reactants and liquid media, someof which would normally be immiscible, at conditions such that at leasta portion of the monomer reacts to produce a polymerization product. Insome embodiments, HSD 40 comprises a colloid mill. Suitable colloidalmills are manufactured by IKA® Works, Inc. Wilmington, N.C. and APVNorth America, Inc. Wilmington, Mass., for example. In some instances,HSD 40 comprises the Dispax Reactor® of IKA® Works, Inc. Several modelsare available having various inlet/outlet connections, horsepower,nominal tip speeds, output rpm, and nominal flow rate. Selection of aparticular device will depend on specific throughput requirements forthe intended application, and on the desired particle size in the outletdispersion from the high shear mixer. In some embodiments, selection ofthe appropriate mixing tools (generators) within HSD 40 may allow forcatalyst size reduction/increase in catalyst surface area.

The high shear device comprises at least one revolving element thatcreates the mechanical force applied to the reactants. The high sheardevice comprises at least one stator and at least one rotor separated bya clearance. For example, the rotors may be conical or disk shaped andare separated from a complementary-shaped stator comprising a pluralityof circumferentially-spaced high shear openings. For example, the rotorsmay be conical or disk shaped and may be separated from acomplementary-shaped stator; both the rotor and stator may comprise aplurality of circumferentially-spaced teeth. In some embodiments, thestator(s) are adjustable to obtain the desired gap between the rotor andthe stator of each generator (rotor/stator set). Grooves in the rotorand/or stator may change directions in alternate stages for increasedturbulence. Each generator may be driven by any suitable drive systemconfigured for providing the necessary rotation.

In some embodiments, the minimum clearance between the stator and therotor is in the range of from about 0.0254 millimeter to about 3.175millimeter (0.001 inch to about 0.125 inch). In certain embodiments, theminimum clearance between the stator and rotor is about 1.524 millimeter(0.060 inch). In certain configurations, the minimum clearance betweenthe rotor and stator is at least 1.778 millimeter (0.07 inch). The shearrate produced by the high shear mixer may vary with longitudinalposition along the flow pathway. In some embodiments, the rotor is setto rotate at a speed commensurate with the diameter of the rotor and thedesired tip speed. In some embodiments, the colloidal mill has a fixedclearance between the stator and rotor. Alternatively, the colloid millhas adjustable clearance.

In some embodiments, HSD 40 comprises a single stage dispersing chamber(i.e., a single rotor/stator combination, a single generator). In someembodiments, high shear device 40 is a multiple stage inline colloidmill and comprises a plurality of generators. In certain embodiments,HSD 40 comprises at least two generators. In other embodiments, highshear device 40 comprises at least 3 high shear generators. In someembodiments, high shear device 40 is a multistage mixer whereby theshear rate (which varies proportionately with tip speed and inverselywith rotor/stator gap) varies with longitudinal position along the flowpathway, as further described herein below.

In some embodiments, each stage of the external high shear device hasinterchangeable mixing tools, offering flexibility. For example, the DR2000/4 Dispax Reactor® of IKA® Works, Inc. Wilmington, N.C. and APVNorth America, Inc. Wilmington, Mass., comprises a three stagedispersing module. This module may comprise up to three rotor/statorcombinations (generators), with choice of fine, medium, coarse, andsuper-fine for each stage. This allows for creation of dispersionshaving a narrow distribution of the desired particle size. In someembodiments, each of the stages is operated with super-fine generator.In some embodiments, at least one of the generator sets has arotor/stator minimum clearance of greater than about 5.08 mm (0.20inch). In some embodiments, at least one of the generator sets has aminimum rotor/stator clearance of greater than about 1.778 mm (0.07inch). In some embodiments the rotors are 60 mm and the stators are 64mm in diameter, providing a clearance of about 4 mm.

Referring now to FIG. 2, there is presented a longitudinal cross-sectionof a suitable high shear device 200. High shear device 200 is adispersing device comprising three stages or rotor-stator combinations,220, 230, and 240. Three rotor/stator sets or generators 220, 230, and240 are aligned in series along drive input 250. The first generator 220comprises rotor 222 and stator 227. The second generator 230 comprisesrotor 223, and stator 228; the third generator 240 comprises rotor 224and stator 229. For each generator the rotor is rotatably driven byinput 250 and rotates, as indicated by arrow 265, about axis 260. Stator227 is fixedly coupled to high shear device wall 255. Each generator hasa shear gap which is the distance between the rotor and the stator.First generator 220, comprises a first shear gap 225; second generator230 comprises a second shear gap 235; and third generator 240 comprisesa third shear gap 245. In some embodiments, shear gaps 225, 235, 245 arebetween about 0.025 mm and 10.0 mm wide. In some embodiments, theprocess comprises utilization of a high shear device 200 wherein thegaps 225, 235, 245 are between about 0.5 mm and about 2.5 mm. In certaininstances the gap is maintained at about 1.5 mm. Alternatively, the gaps225, 235, 245 are different for generators 220, 230, 240. In certaininstances, the gap 225 for the first generator 220 is greater than aboutthe gap 235 for the second generator 230, which is in turn greater thanabout the gap 245 for the third generator. As mentioned above, thegenerators of each stage may be interchangeable, offering flexibility.

Generators 220, 230, and 240 may comprise a coarse, medium, fine, andsuper-fine characterization. Rotors 222, 223, and 224 and stators 227,228, and 229 may be toothed designs. Each generator may comprise two ormore sets of rotor-stator teeth. Rotors 222, 223, and 224 may comprise anumber of rotor teeth circumferentially spaced about the circumferenceof each rotor. Stators 227, 228, and 229 may comprise a number ofcomplementary stator teeth circumferentially spaced about thecircumference of each stator. In embodiments, the inner diameter of therotor is about 11.8 cm. In embodiments, the outer diameter of the statoris about 15.4 cm. In certain embodiments, each of three stages isoperated with a super-fine generator, comprising a shear gap of betweenabout 0.025 mm and about 3 mm. For applications in which solid particlesare to be sent through high shear device 200, shear gap width may beselected for reduction in particle size and increase in particle surfacearea. In some embodiments, the disperser is configured so that the shearrate will increase stepwise longitudinally along the direction of theflow. The IKA® model DR 2000/4, for example, comprises a belt drive, 4Mgenerator, PTFE sealing ring, inlet flange 25.4 mm (1 inch) sanitaryclamp, outlet flange 19 mm (¾ inch) sanitary clamp, 2HP power, outputspeed of 7900 rpm, flow capacity (water) approximately 300-700 L/h(depending on generator), a tip speed of from 9.4-41 m/sec (1850 ft/minto 8070 ft/min).

Reactor/Vessel. Vessel or reactor 10 is any type of vessel in which amultiphase reaction can be propagated to carry out the above-describedconversion reaction(s). For instance, vessel 10 may be a continuous orsemi-continuous stirred tank reactor, or it may comprise one or morebatch reactors arranged in series or in parallel. In other embodiments,vessel 10 may be a tower reactor, a tubular reactor or multi-tubularreactor. One or more line 15 may be connected to vessel 10 forintroducing monomer, solvent, initiator or catalyst, or other material,as desired for particular applications.

Vessel 10 may include one or more of the following items: stirringsystem, heating and/or cooling capabilities, pressure measurementinstrumentation, temperature measurement instrumentation, one or moreinjection points, and level regulator (not shown), as are known in theart of reaction vessel design. For example, a stirring system mayinclude a motor driven mixer. A heating and/or cooling apparatus maycomprise, for example, a heat exchanger. Alternatively, as much of thepolymerization reaction may occur within HSD 40, in some embodiments,vessel 10 may serve primarily as a storage vessel in some cases.Although generally less desired, in some applications vessel 10 may beomitted, particularly if multiple high shear mixers/reactors areemployed in series, as further described below. Line 16 is connected tovessel 10 for withdrawal or removal of the polyvinyl chloride product.

Heat Transfer Devices. In addition to the above-mentionedheating/cooling capabilities of vessel 10, other external or internalheat transfer devices for heating or cooling a process stream are alsocontemplated in variations of the embodiments illustrated in FIG. 1.Some suitable locations for one or more such heat transfer devices arebetween pump 5 and HSD 40, between HSD 40 and vessel 10, and betweenvessel 10 and pump 5 when system 1 is operated in multi-pass mode. Somenon-limiting examples of such heat transfer devices are shell, tube,plate, and coil heat exchangers, as are known in the art.

Pumps. Pump 5 is configured for either continuous or semi-continuousoperation, and may be any suitable pumping device that is capable ofproviding greater than 203 kPa (2 atm) pressure, preferably greater than304 kPa (3 atm) pressure, to allow controlled flow through HSD 40 andsystem 1. For example, a Roper Type 1 gear pump, Roper Pump Company(Commerce Ga.) Dayton Pressure Booster Pump Model 2P372E, DaytonElectric Co (Niles, Ill.) is one suitable pump. Preferably, all contactparts of the pump comprise stainless steel. If corrosive substances areto be pumped it may be desirable to provide gold plated contactsurfaces. In some embodiments of the system, pump 5 is capable ofpressures greater than about 2027 kPa (20 atm). In addition to pump 5,one or more additional, high pressure pumps (not shown) may be includedin the system illustrated in FIG. 1. For example, a booster pump, whichmay be similar to pump 5, may be included between HSD 40 and vessel 10for boosting the pressure into vessel 10. As another example, asupplemental feed pump, which may be similar to pump 5, may be includedin line 15 for introducing additional monomer, solvent, initiator orcatalyst into vessel 10. In some embodiments, line 16 may be joined toline 21 for multi-pass operation, as further described herein below. Asstill another example, a compressor type pump may be positioned betweenline 17 and HSD 40 for recycling unreacted gases from vessel 10 to aninlet of the high shear device.

Process for Production of Polyvinyl Chloride

In operation for the production of polyvinyl chloride by free radicalpolymerization of vinyl chloride, a stream of liquid vinyl chloridemonomer is introduced into system 1 via line 21, is pumped through 13and fed into HSD 40. An initiator or catalyst stream introduced via line22 is combined with the monomer in line 13. The initiator or catalystmay be dissolved or suspended in monomer or in an aqueous or nonaqueoussolvent. Alternatively, the initiator stream may be fed directly intoHSD 40 instead of being combined with the monomer in line 13.

The process may be operated in either continuous or semi-continuous flowmode, or it may be operated in batch mode. Pump 5 is operated to pumpthe liquid reactant (monomer solution) from line 21, and to buildpressure and feed HSD 40, providing a controlled flow through line 13and high shear mixer (HSD) 40, and throughout high shear system 1. Insome embodiments, pump 5 increases the pressure of the monomer stream togreater than 203 kPa (2 atm), preferably greater than about 304 kPa (3atm). In some applications, pressures greater than about 2027 kPa (20atm) may be used to accelerate reactions, with the limiting factor beingthe pressure limitations of the selected pump 5 and high shear mixer 40.The solution in line 13 comprises vinyl chloride monomer, and,optionally, an aqueous or non-aqueous solvent, for the free radicalpolymerization of the vinyl chloride, facilitated by an initiator orcatalyst, to form polyvinyl chloride.

Alternatively, the vinyl chloride and solvent may be initiallyintroduced into vessel 10 via one or more feed line 15, and, after beingmixed, are fed into line 21. The contents of vessel 10 are maintained ata specified bulk reaction temperature using suitable heating and/orcooling capabilities (e.g., cooling coils) and temperature measurementinstrumentation. For example, since vinyl chloride exists as a gas atambient temperature and pressure, system 1 may be sufficientlypressurized to maintain the vinyl chloride monomer in solution or inliquid phase at a given temperature. Pressure in the vessel may bemonitored using suitable pressure measurement instrumentation, and thelevel of reactants in the vessel may be controlled using a levelregulator (not shown), employing techniques that are known to those ofskill in the art. The contents are stirred or circulated continuously orsemi-continuously.

Initiator. A solution containing a suitable polymerization initiator, ora catalyst, dissolved in a suitable aqueous or non-aqueous solvent, iscombined with the monomer stream in line 13, by introduction throughline 22. In some embodiments, the free radical initiator is an organicperoxide compound such as t-butyl hydroperoxide, lauroyl peroxide,benzoyl peroxide or isopropylperoxy dicarbonate, for example. If a solidcatalyst is employed, it may be introduced via line 22 as a slurry in asuitable aqueous or non-aqueous solvent. In some embodiments, theselected mixing tools (i.e., rotor/stator sets or generators) in HSD 40are selected for catalyst size reduction and/or increase in catalystsurface area.

In some embodiments, monomer solution is continuously pumped into line13 to form the high shear mixer feed stream. Additional solvent may beintroduced into line 13, and, in some embodiments, monomer solution orsolvent may be introduced independently into HSD 40. The actual ratio ofthe raw materials used is determined based on the desired selectivityand operating temperatures and pressures. Pressure is preferably kepthigh enough to keep the monomer in solution. For the purposes of thisdisclosure, the terms “superficial pressure” and “superficialtemperature” refer to the apparent, bulk, or measured pressure ortemperature, respectively, in a vessel, conduit or apparatus of thesystem. The actual temperatures and/or pressures at which the reactantsmake contact and react in the microenvironment of a transient cavityproduced by the hydrodynamic forces of the high shear mixer may be quitedifferent, as further discussed elsewhere herein. For bulkpolymerization embodiments, 100% monomer may be used. Alternatively, theliquid vinyl chloride stream may also include a suitable solvent. Insolution polymerization an organic solvent is used, and in emulsionpolymerization the ingredients may be predispersed to make an emulsion,and polymerization occurs in the colloidal emulsion. Accordingly, insome embodiments the reaction may comprise a homogeneous liquid phasereaction in which the vinyl chloride monomer and an aqueous initiatorsolution are in the form of a very fine emulsion.

After pumping, the initiator and monomer liquid phase are mixed withinHSD 40, which provides superior dissolution into solution and/orenhancement of reactant mixing. In some embodiments it may create a finemixture, emulsion or dispersion of the reactants, which may also includecatalyst and/or an otherwise immiscible solvent. As used herein, theterm “dispersion” refers to a liquefied mixture that contains twodistinguishable substances (or phases) that will not readily mix anddissolve together. A dispersion comprises a continuous phase (ormatrix), which holds therein discontinuous droplets, bubbles, and/orparticles of the other phase or substance. The term dispersion may thusrefer to foams comprising gas bubbles suspended in a liquid continuousphase, emulsions in which droplets of a first liquid are dispersedthroughout a continuous phase comprising a second liquid with which thefirst liquid is immiscible, and continuous liquid phases throughoutwhich solid particles are distributed. The term “dispersion” encompassescontinuous liquid phases throughout which gas bubbles are distributed,continuous liquid phases throughout which solid particles (e.g., solidcatalyst) are distributed, continuous phases of a first liquidthroughout which droplets of a second liquid that is substantiallyinsoluble in the continuous phase are distributed, and liquid phasesthroughout which any one or a combination of solid particles, immiscibleliquid droplets, and gas bubbles are distributed. Hence, a dispersioncan exist as a homogeneous mixture in some cases (e.g., liquid/liquidphase), or as a heterogeneous mixture (e.g., gas/liquid, solid/liquid,or gas/solid/liquid), depending on the nature of the materials selectedfor combination.

In some embodiments, nanoparticles and microparticles containingcatalyst or another immiscible component are formed by HSD 40. Forexample, disperser IKA® model DR 2000/4, a high shear, three stagedispersing device configured with three rotors in combination withstators, aligned in series, is used to create a dispersion of catalystin liquid medium comprising monomer and any initiators (i.e., “thereactants”). The rotor/stator sets may be configured as illustrated inFIG. 2, for example. For some applications, the direction of rotation ofthe generators may be opposite that shown by arrow 265 (e.g., clockwiseor counterclockwise about axis of rotation 260). The combined reactantsentering the high shear mixer via line 13 proceed to a first stagerotor/stator combination having circumferentially spaced first stageshear openings. In some applications, the direction of flow of thereactant stream entering inlet 205 corresponds to the axis of rotation260. The coarse dispersion exiting the first stage enters the secondrotor/stator stage, having second stage shear openings. The reducedparticle-size dispersion emerging from the second stage enters the thirdstage rotor/stator combination having third stage shear openings. Thedispersion exits the high shear mixer via line 19. In some embodiments,the shear rate increases stepwise longitudinally along the direction ofthe flow. For example, in some embodiments, the shear rate in the firstrotor/stator stage is greater than the shear rate in subsequentstage(s). In other embodiments, the shear rate is substantially constantalong the direction of the flow, with the stage or stages being thesame. If the high shear mixer includes a PTFE seal, for example, theseal may be cooled using any suitable technique that is known in theart. For example, the reactant stream flowing in line 13 may be used tocool the seal and in so doing be preheated as desired prior to enteringthe high shear mixer.

The rotor of HSD 40 is set to rotate at a speed commensurate with thediameter of the rotor and the desired tip speed (e.g., in the range ofabout 9.4-41 m/sec (about 1850 ft/min to about 8070 ft/min)). Asdescribed above, the high shear mixer (e.g., colloid mill) has either afixed clearance between the stator and rotor or has adjustableclearance. HSD 40 serves to intimately mix the reactants. In someembodiments of the process, the transport resistance of the reactants isreduced by operation of the high shear mixer such that the velocity ofthe polymerization reaction is increased by greater than a factor of 5.In some embodiments, the velocity of the reaction is increased by atleast a factor of 10. In some embodiments, the velocity is increased bya factor in the range of about 10 to about 100 fold. In someembodiments, HSD 40 delivers at least 300 L/h with a power consumptionof 1.5 kW at a nominal tip speed of at least 22.9 m/sec (4500 ft/min),and which may exceed 40 m/sec (7900 ft/min). In some embodiments, themixture is subjected to a shear rate greater than 20,000 s⁻¹.

Although measurement of instantaneous temperature and pressure at thetip of a rotating shear unit or revolving element in HSD 40 isdifficult, it is estimated that the localized temperature seen by theintimately mixed reactants is in excess of 500° C. and at pressures inexcess of 5000 kPa (50 atm) under cavitation conditions. When animmiscible solid (e.g., catalyst) or immiscible liquid (e.g., aqueoussolvent) is present, the high shear mixing results in dispersion of thecatalyst or aqueous solvent in micron or submicron-sized particles(i.e., mean diameter less than one micron). In some embodiments, theresultant dispersion has an average droplet or particle size less thanabout 1.5 μm. In some embodiments, the average size is less than onemicron in diameter. In some embodiments, the mean droplet or particlesize is in the range of about 0.4 μm to about 1.5 μm. In someembodiments, the mean droplet or particle size is less than about 400nm, in the range of about 200 nm to about 400 nm, or is about 100 nm insome cases. Without wishing to be limited by theory, it is believed thatsub-micron particles or bubbles dispersed in a liquid undergo movementprimarily through Brownian motion effects. The bubbles in the productdispersion created by HSD 40 may have greater mobility through boundarylayers of catalyst particles, if present, thereby facilitating andaccelerating the polymerization reaction through enhanced transport ofreactants.

For the purposes of this disclosure, a nanodispersion is a dispersion ofimmiscible liquid-liquid phases or heterogeneous solid-liquid phases inwhich the sizes of the droplets or particles in the dispersed phase areless than 1000 nanometers (i.e., <1 micron). A nanodispersion issometimes also referred to herein as a “dispersion.” In manyembodiments, the nanodispersion is able to remain dispersed atatmospheric pressure for at least 15 minutes.

The resulting high shear mixture exits HSD 40 via line 19 and feeds intovessel 10, as illustrated in FIG. 1, wherein polymerization occurs orcontinues to take place. If desired, the high shear mixture may befurther processed prior to entering vessel 10. For example, furthermixing in one or more successive high shear mixing devices, similar toHSD 40 with the same or different generator configurations, may beperformed before the process stream enters reactor/vessel 10. Ifdesired, one or more additives may be injected at line 13 or 18, or anyother suitable point in the process, or as illustrated in the flowdiagram shown in FIG. 1. In some embodiments, a homogeneous free radicalpolymerization reaction takes place. In some other embodiments, aheterogeneous reaction takes place in which the intimately mixed monomersolution and finely divided catalyst, or immiscible initiator solution,are in the form of a highly dispersed liquid or nanoemulsion.

In some embodiments, as a result of the intimate mixing of the reactantsprior to entering reactor 10, a significant portion of the chemicalreaction may take place in HSD 40, with or without the presence ofcatalyst. Polymerization of monomer to the corresponding polymer willoccur whenever suitable time, temperature and pressure conditions exist,facilitated in some cases by the presence of the catalyst and/orinitiator. In this sense the polymerization of monomer may occur at anypoint in the flow diagram of FIG. 1 if temperature and pressureconditions are suitable. The polymerization reaction may take place inthe high shear mixer to a significant extent. A discrete reactor isusually desirable, however, to allow for increased residence time,agitation and heating and/or cooling of the bulk reactants. Accordingly,in some embodiments, reactor/vessel 10 may be used primarily for heatingand separation of volatile reaction products (i.e., vent gas) from thepolymerization product. Alternatively, or additionally, vessel 10 mayserve as a primary reaction vessel where most of the polymer isproduced. For example, the process may be operated as a single pass or“once through” process in order to minimize subjecting the formedpolymer to shearing, in which case vessel 10 may serve as the primaryreaction vessel. Vessel/reactor 10 may be operated in either continuousor semi-continuous flow mode, or it may be operated in batch mode.

As mentioned above, the contents of vessel 10 may be maintained at aspecified reaction temperature using heating and/or cooling capabilities(e.g., cooling coils) and temperature measurement instrumentation.Pressure in the vessel may be monitored using suitable pressuremeasurement instrumentation, and the level of reactants in the vesselmay be controlled using a level regulator (not shown), employingtechniques that are known to those of skill in the art. The contents arestirred continuously or semi-continuously. The bulk or global operatingtemperature of the reactants is desirably maintained below their flashpoints. In some embodiments, the operating conditions of system 1comprise a temperature in the range of from about 20° C. to about 230°C. In some embodiments, the temperature is less than about 200° C. Insome embodiments, the temperature is in the range of from about 160° C.to 180° C. In specific embodiments, the reaction temperature in vessel10, in particular, is in the range of from about 155° C. to about 160°C. In some embodiments the process is operated at ambient temperature.In some embodiments, the reaction pressure in vessel 10 is in the rangeof from about 203 kPa to about 6080 kPa (about 2 atm to about 55-60atm). In some embodiments, reaction pressure is in the range of fromabout 811 kPa to about 1520 kPa) (about 8 atm to about 15 atm). In someembodiments, the reaction pressure is less than 600 kPa (6 atm). Thesuperior dissolution and/or dispersion provided by the external highshear mixing potentially allows a decrease in operating pressure whilemaintaining or even increasing reaction rate. Operating thepolymerization process at decreased pressure potentially decreases wearof the materials constituting the reactors, the piping, and themechanical parts of the plant, as well as the ancillary devices, in someembodiments of the high shear enhanced polymerization process.

The polymerization product may be produced either continuously,semi-continuously or batch wise, as desired, and is removed from system1 via product line 16. In some embodiments, more than one reactorproduct line 16 is used to remove the product. Vent gas, containingunconverted gaseous vinyl chloride and any volatile side reactionproducts, for example, exit reactor 10 via line 17. The product streamcomprising polyvinyl chloride and dissolved, unconverted monomer exitsreactor 10 by line 16. In some embodiments, the content of unconvertedvinyl chloride in this product stream is reduced compared to that ofconventional PVC production methods. In some embodiments the productstream is further processed. For example, the content of unconvertedmonomer in the product stream may be reduced using suitable techniquesas are known. The polymerized PVC granules may be filtered orcentrifuged out, in the case of solution polymerization, and theunpolymerized liquid monomer recycled through the high shear mixingdevice. In the case of bulk polymerization, the residual vinyl chloridemonomer may be stripped off and recycled through the high shear mixingdevice. The PVC product may be used to manufacture any of a wide varietyof commercial products. For instance, it may serve as the raw materialfor making clothing, upholstery, plumbing pipe, vinyl flooring and otherbuilding materials. The vent gas may be further treated and vented, orits components may be recycled, as desired, using known techniques.

Multiple Pass Operation. Referring still to FIG. 1, the system isconfigured for either single pass or multi-pass operation, wherein,after the initial preparation of the monomer-solvent solution in vessel10 and commencement of the process, the output from line 16 of vessel 10goes directly to recovery of the polymer product or to furtherprocessing. In some embodiments it may be desirable to pass the contentsof vessel 10, or a portion thereof containing unreacted monomersolution, through HSD 40 during a second pass. In this case, all or aportion of the output from vessel 10 may be returned by connecting line16 to line 21 or line 13, for further dispersion and reaction in HSD 40.Additional initiator or catalyst slurry may be injected via line 22 intoline 13, or it may be added directly into the high shear mixer (notshown), if needed. Additional solvent or monomer may be injected at line21, as needed, for a particular application.

Multiple High Shear Mixing Devices. In some embodiments, two or morehigh shear devices like HSD 40, or configured differently, are alignedin series, and are used to further enhance the reaction. Their operationmay be in either batch or continuous mode. In some instances in which asingle pass or “once through” process is desired, the use of multiplehigh shear devices in series may also be advantageous. For instance, insome applications, where low density product containing shorter polymerchains is desired, the product may be recycled via line 21, to pump 5,and through high shear mixer 40, before returning via line 18 to vessel10. In some embodiments where multiple high shear devices are operatedin series, vessel 10 may be omitted. When multiple high shear devicesare operated in series, additional reactant(s) may be injected into theinlet feed stream of each device. In some embodiments, multiple highshear devices 40 are operated in parallel, and the outlet dispersionstherefrom are introduced into one or more vessel 10.

The application of enhanced mixing of the reactants by HSD 40potentially causes greater polymerization of the monomer in someembodiments of the process. In some embodiments, the enhanced mixingpotentiates an increase in throughput of the process stream. In someembodiments, the high shear mixing device is incorporated into anestablished process, thereby enabling an increase in production (i.e.,greater throughput). In contrast to some existing methods that attemptto increase the degree of polymerization by increasing reactorpressures, the superior dissolution and/or dispersion provided byexternal high shear mixing may allow in many cases a decrease in overalloperating pressure while maintaining or even increasing thepolymerization rate. Without wishing to be limited to a particulartheory, it is believed that the level or degree of high shear mixing issufficient to increase rates of mass transfer and may also producelocalized non-ideal conditions that enable reactions to occur that mightnot otherwise be expected to occur based on Gibbs free energypredictions. Localized non ideal conditions are believed to occur withinthe high shear device resulting in increased temperatures and pressureswith the most significant increase believed to be in localizedpressures. The increase in pressures and temperatures within the highshear device are instantaneous and localized and quickly revert back tobulk or average system conditions once exiting the high shear device. Insome cases, the high shear mixing device induces cavitation ofsufficient intensity to dissociate one or more of the reactants intofree radicals, which may intensify a chemical reaction or allow areaction to take place at less stringent conditions than might otherwisebe required. Cavitation may also increase rates of transport processesby producing local turbulence and liquid micro-circulation (acousticstreaming). An overview of the application of cavitation phenomenon inchemical/physical processing applications is provided by Gogate et al.,“Cavitation: A technology on the horizon,” Current Science 91 (No. 1):35-46 (2006). The high shear mixing device of certain embodiments of thepresent system and methods is operated under what is believed to becavitation conditions effective to dissociate the initiator and monomersinto free radicals, which then react to form the polymer.

In some embodiments, use of an above-described high shear process allowsfor greater catalyzed polymerization of monomer to polymerizationproduct and/or an increase in throughput of the reactants. In someembodiments, an external high shear mixing device is incorporated intoan established process, thereby making possible an increase inproduction compared to the process operated without the high shearmixing of the reactants. In some embodiments, a disclosed process orsystem makes possible the design of a smaller and/or less capitalintensive process than previously possible without the incorporation ofthe external high shear mixing device. In some embodiments, theapplication of a disclosed method potentially reduces operatingcosts/increases production from an existing process. In certainembodiments, the use of a disclosed method may reduce capital costs forthe design of new polymerization processes. Still other potentialbenefits of some embodiments of the system and method for the productionof polyvinyl chloride include, but are not limited to, faster cycletimes, increased throughput, higher monomer conversion, reducedoperating costs and/or reduced capital expense due to the possibility ofdesigning smaller reactors and/or operating the polymerization processat lower temperature and/or pressure. In some embodiments, apolymerization method is provided for the production of polyvinylchloride, without the need for large volume reactors and without theneed to recover substantial amounts of unconverted monomer.

While preferred embodiments of the invention have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the spirit and teachings of the invention. Theembodiments described herein are exemplary only, and are not intended tobe limiting. Many variations and modifications of the inventiondisclosed herein are possible and are within the scope of the invention.Where numerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4,etc.; greater than 0.10 includes 0.11, 0.12, 0.13, and so forth). Use ofbroader terms such as comprises, includes, having, etc. should beunderstood to provide support for narrower terms such as consisting of,consisting essentially of, comprised substantially of, and the like.

Accordingly, the scope protection is not limited by the description setout above but is only limited by the claims which follow, that scopeincluding all equivalents of the subject matter of the claims. Each andevery original claim is incorporated into the specification as anembodiment of the present invention. Thus, the claims are a furtherdescription and are an addition to the preferred embodiments of thepresent invention. The disclosures of all patents, patent applications,and publications cited herein are hereby incorporated by reference, tothe extent they provide exemplary, procedural or other detailssupplementary to those set forth herein.

1-18. (canceled)
 19. A system for production of polyvinyl chloride, thesystem comprising: a high shear mixing device comprising at least onerotor/stator set configured to produce a polymerization mixture by highshear mixing a vinyl chloride solution with an initiator solution,wherein the polymerization mixture comprises an emulsion of droplets andwherein high shear mixing comprises a rotor tip speed of at least 5.1m/sec; a pump in fluid communication with an inlet of said high shearmixing device; and a vessel in fluid communication with an outlet ofsaid high shear mixing device and configured for maintaining apredetermined pressure and temperature on the polymerization mixture.20. The system of claim 19, wherein said the high shear mixing device isconfigured to produce a shear rate of at least 20,000 s⁻¹.
 21. Thesystem of claim 19 wherein said high shear mixing device is configuredfor operating at a flow rate of at least 300 L/h at said tip speed of atleast 22.9 m/sec.
 22. The system of claim 19, wherein said high shearmixing device is configured to provide an energy expenditure greaterthan 1000 W/m³.
 23. The system of claim 19 comprising at least two saidhigh shear mixing devices.
 24. The system of claim 19 wherein saidvessel comprises a tank reactor.
 25. The system of claim 19 wherein thehigh shear mixing device comprises an enclosure enclosing saidrotor/stator set and configured for maintaining a predetermined pressureon a reaction mixture within the high shear mixing device duringoperation.
 26. The system of claim 19 wherein the at least one highshear mixing device comprises at least two rotor/stator sets.
 27. Thesystem of claim 26 wherein a first rotor/stator set is configured toproduce a first shear rate and a second rotor/stator set is configuredto produce a second shear rate, wherein the shear rate is defined as thetip speed of the rotor divided by the minimum clearance between therotor and the stator, and wherein passage of fluid through the highshear mixing device comprises passing through said first rotor/statorset prior to passing through said second rotor/stator set.
 28. Thesystem of claim 27 wherein the first shear rate is different from thesecond shear rate.
 29. The system of claim 28 wherein the first shearrate is less than the second shear rate.
 30. The system of claim 20,wherein said high shear mixing device is configured to produce a shearrate in the range of from 20,000 s⁻¹ to 100,000 s⁻¹.
 31. The system ofclaim 20 wherein said high shear mixing device is configured to producea shear rate of at least 1,600,000 s⁻¹.
 32. The system of claim 19wherein the pump is operable to provide vinyl chloride solution to thehigh shear mixing device at a pressure of greater than 203 kPa (2 atm).33. The system of claim 32 wherein the pump is operable to provide vinylchloride solution to the high shear mixing device at a pressure ofgreater than 304 kPa (3 atm).
 34. The system of claim 33 wherein thepump is operable to provide vinyl chloride solution to the high shearmixing device at a pressure of greater than 2027 kPa (20 atm).
 35. Thesystem of claim 23 wherein at least two high shear mixing devices arealigned in series.
 36. The system of claim 23 wherein at least two highshear mixing devices are aligned in parallel.
 37. The system of claim 19wherein a rotor and a stator of the at least one rotor/stator set areseparated by a minimum clearance in the range of from about 0.025 mm toabout 10 mm.
 38. The system of claim 37 wherein the minimum clearance isin the range of from about 0.5 to about 2.5 mm.